Gas fired hot air furnaces have long been used to heat spaces in both residential and commercial settings. Most conventional gas fired furnaces include a plurality of heat exchangers, spaced apart to allow air flow therebetween. The heat exchangers define an internal flow path for hot combustion gases supplied by burners. Heat transferred through the heat exchangers may be used to effect heating of a particular area.
A common arrangement for gas fired furnaces is to provide an individual burner associated with each heat exchanger. This arrangement is shown schematically in FIG. 1. A fuel gas mixture 10 is delivered through a manifold 12. The manifold has a plurality of outlets 14 corresponding with the number of heat exchangers 16 employed in the furnace. Interposed between the heat exchangers and the manifold outlets are a plurality of burners 18 provided in one-to-one correspondence to the number of heat exchangers. The burners may be of conventional construction of the type shown in U.S. Pat. No. 6,196,835 which is incorporated by reference herein for all purposes. Each burner includes a venturi device which provides for the proper mixture of air and fuel. The air and fuel is combined at one end of the burner 18 adjacent the manifold 12 and the air/fuel mixture is ignited adjacent the opposite end of the burner 18 at a burner face 18a. The hot combustion gases enter each heat exchanger and are caused to flow in a tortuous path within each heat exchanger.
The individual burner/heat exchanger arrangement is more particularly shown in U.S. Pat. No. 4,467,780 and is generally described herein with reference to FIG. 2. As shown in FIG. 2, the typical hot air furnace 20 has a sheet metal outer covering 22 which encases a series of five heat exchangers 24, blower 26, burners 28, one burner for each heat exchanger 24, and a pressure regulator 30. The gas/air mixture is injected by burner 18 into the open end of a heat exchanger 24. As a part of the injection process, additional air is drawn into the heat exchanger 24 so that the gas may be fully combusted within the heat exchanger 24. A header 32 is connected to the exhaust portion of each of the heat exchangers 24, header 22 also being connected to an induction draft fan 34 which creates a negative pressure through the heat exchangers 24 and a positive exhaust pressure to discharge the gases resulting from combustion through opening 36 to the discharge flue. Blower 26 receives cold room air from the area which is to be heated, forces that air over the heat exchanger surfaces in the direction indicated by arrow 38, the air then being collected and returned to the rooms to be heated.
It should be appreciated that the arrangement shown in FIG. 2 requires multiple burners to be provided so that each heat exchanger employs an associated burner. Use of multiple burners generally increases the cost of the furnace unit. Furthermore, as multiple burners must be individually ignited, a manifold must be used to bring the gas fuel to the burner. The manifold must employ specifically configured orifices at the openings 14 to provide the proper amount of gas to each burner. The manufacture and maintenance of this manifold device also increases the cost of manufacture and maintenance of the furnace. Furthermore, in certain situations there is a desire to switch between two types of fuel sources such as natural gas and propane. The manifold devices are specifically manufactured to handle one type of fuel source. Accordingly, a conversion from one fuel source to another may require the alteration or replacement of the burners. Furthermore, the efficient operation of the furnace depends largely on the proper burning of each burner. In a multiple burner situation, it is often difficult to detect improper operation of an individual burner. Improper operation of any individual burner may result in the creation of undesirable combustion products and/or reduce the operating life of the heat exchanger.